enh(JavaScription): refactor doubly link list (#629)
atulll
GitHub
parent
a88e14cb8a
commit
d38e965e1b
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@ -1,167 +1,256 @@
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function DoubleLinkedList() {
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function Node(val) {
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const Node = function(element) {
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this.value = val;
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this.element = element;
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this.next = null;
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this.next = null;
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this.previous = null;
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this.prev = null;
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};
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let length = 0;
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const head = new Node('head');
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let tail = head;
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// Add new element
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this.append = function(element) {
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const node = new Node(element);
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node.prev = tail;
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tail.next = node;
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tail = node;
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length++;
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};
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// Add element
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this.insert = function(position, element) {
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// Check of out-of-bound values
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if (position >= 0 && position <= length) {
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const node = new Node(element);
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let current = head;
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let index = 0;
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while (index < position) {
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current = current.next;
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index++;
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}
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node.next = current.next;
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if (node.next !== null) {
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node.next.prev = node;
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}
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node.prev = current;
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current.next = node;
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length++;
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return true;
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} else {
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return null;
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}
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};
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// Remove element at any position
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this.removeAt = function(position) {
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// look for out-of-bounds value
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if (position > -1 && position < length) {
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let removedNode;
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let current = head;
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let index = 0;
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while (index < position) {
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current = current.next;
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index++;
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}
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if (current.next) {
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removedNode = current.next;
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}
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if (current.next.next !== null) {
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current.next.next.prev = current;
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}
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current.next = current.next.next;
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// if current.next is null, that means it
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// is the last elem, so let's mark it as tail.
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if (!current.next) {
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tail = current;
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}
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length--;
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return removedNode.element;
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} else {
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return null;
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}
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};
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// Get the indexOf item
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this.indexOf = function(elm) {
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let current = head;
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let index = -1;
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// If element found then return its position
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while (current.next) {
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if (elm === current.next.element) {
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return ++index;
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}
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index++;
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current = current.next;
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}
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// Else return -1
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return -1;
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};
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// Delete an item from the list
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this.delete = (elm) => {
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return this.removeAt(this.indexOf(elm));
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};
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this.toString = function() {
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let current = head.next;
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let string = '';
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while (current) {
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string += current.element + ' ';
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current = current.next;
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}
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return string;
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};
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// Convert list to array
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this.toArray = function() {
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const arr = [];
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let current = head.next;
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while (current) {
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arr.push(current.element);
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current = current.next;
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}
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return arr;
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};
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// Check if list is empty
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this.isEmpty = function() {
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return length === 0;
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};
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// Get the size of the list
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this.size = function() {
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return length;
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};
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// Get the head
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this.getHead = function() {
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return head.next;
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};
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// Get the tail
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this.getTail = function() {
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return tail;
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};
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}
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}
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const newDoubleLinkedList = new DoubleLinkedList();
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function DoubleLinkList() {
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newDoubleLinkedList.append(1);
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// Initially when we create an object of DoubleLinkList(DLL),
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newDoubleLinkedList.append(5);
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// we will want it to be an empty object
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newDoubleLinkedList.append(3);
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// i.e its length will be 0 and head and tail will be null.
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newDoubleLinkedList.append(20);
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this.length = 0;
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newDoubleLinkedList.insert(1, 9);
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this.head = this.tail = null;
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newDoubleLinkedList.removeAt(2);
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}
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console.log(newDoubleLinkedList.toArray());
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// A DLL will only have
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console.log(newDoubleLinkedList.toString());
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// length, head and tail, all the other methods will be one level up.
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DoubleLinkList.prototype.append = function(val) {
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if (val) {
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// Create a new node by passing it the value which the user has passed.
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const newNode = new Node(val);
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newDoubleLinkedList.delete(20);
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// Check if the head is null, if it is
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console.log('After delete 20: ' + newDoubleLinkedList.toString());
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// that means this is the first entry, hence assign
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console.log(`Tail points to : ${newDoubleLinkedList.getTail().element}`);
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// hence make the newNode as the head and tail.
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if (!this.head) {
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this.head = this.tail = newNode;
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} else {
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// elsepart: if the head and tail is not null
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// then take the next pointer of tail and connect it to newNode
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this.tail.next = newNode;
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// take the previous pointer of the newNode and connect it to tail.
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newNode.previous = this.tail;
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// Now we have connected the newNode to DLL, so lets
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// So let's make the newNode as the tail.
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this.tail = newNode;
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}
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// finally increment the length of DLL.
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this.length++;
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return this;
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}
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return null;
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};
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// inserts a new node into dll at a particular position.
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DoubleLinkList.prototype.insertAt = function(val, position = 0) {
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if (!this.head && position !== 0) return null;
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const newNode = new Node(val);
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let currentNode = this.head;
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// Boolean flag to keep track of whether we are updating
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// the dll or not, so that common code related to updation
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// is not written more than once.
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let isNodeInserted = false;
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// If position is 0 and head is empty i.e dll is empty
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// so we are assigning the newNode to head and tail
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// else we are assigning the next of newNode to head,
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// previous of head to newNode and eventually
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// we are making the head as the newNode.
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if (position === 0) {
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if (!this.head) {
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this.head = this.tail = newNode;
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} else {
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currentNode = this.head;
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newNode.next = currentNode;
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currentNode.previous = newNode;
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this.head = newNode;
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isNodeInserted = true;
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}
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}
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// Check if the position is valid.
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if (position > 0 && position <= this.length) {
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let idx = 0;
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// iterate to the node just before the position.
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while (idx < position - 1) {
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if (currentNode.next) {
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currentNode = currentNode.next;
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}
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idx++;
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}
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newNode.previous = currentNode;
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newNode.next = currentNode.next;
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currentNode.next = newNode;
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// If newNode.next exists, we are assigning its previous
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// to newNode, else we are making the newNode as tail.
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if (newNode.next) {
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newNode.next.previous = newNode;
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} else {
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this.tail = newNode;
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}
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isNodeInserted = true;
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}
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// Common code if the insertion succeeds.
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if (isNodeInserted) {
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this.length++;
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}
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// Now this is very important we are returning the instance
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// i.e the dll so that we can do something like method chaining.
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return this;
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};
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// Remove an element from a particular position in dll.
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DoubleLinkList.prototype.removeAt = function(position) {
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if (position === null || position === undefined) return null;
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// checking if the dll is empty or the position is out of bounds.
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if (!this.head || position < 0 || position > this.length) return null;
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let currentNode = this.head;
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let iteration = 0;
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// iterating until we find the position.
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while (iteration !== position) {
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if (currentNode.next) {
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currentNode = currentNode.next;
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}
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iteration++;
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}
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let previousNode = null;
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let nextNode = null;
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if (currentNode.previous) {
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previousNode = currentNode.previous;
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}
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if (currentNode.next) {
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nextNode = currentNode.next;
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}
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if (previousNode) {
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previousNode.next = nextNode;
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if (currentNode === this.tail) {
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this.tail = previousNode;
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}
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}
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if (nextNode) {
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nextNode.previous = previousNode;
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if (currentNode === this.head) {
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this.head = nextNode;
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}
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}
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this.length--;
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return currentNode;
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};
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DoubleLinkList.prototype.indexOf = function(elm) {
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if (!this.head) return null;
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let currentNode = this.head;
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let idx = 0;
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while (currentNode) {
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if (currentNode.value === elm) {
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return idx;
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}
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idx++;
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currentNode = currentNode.next;
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}
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return null;
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};
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DoubleLinkList.prototype.delete = function(elm) {
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const idx = this.indexOf(elm);
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return this.removeAt(idx);
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};
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DoubleLinkList.prototype.toArray = function() {
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if (!this.head) return null;
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const arr = [];
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let currentNode = this.head;
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while (currentNode) {
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arr.push(currentNode.value);
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currentNode = currentNode.next;
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}
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return arr;
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};
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DoubleLinkList.prototype.toString = function() {
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if (!this.head) return null;
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let currentNode = this.head;
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let returnString = '';
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while (currentNode) {
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returnString += currentNode.value + ' ';
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currentNode = currentNode.next;
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}
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return returnString;
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};
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DoubleLinkList.prototype.isEmpty = function() {
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return this.length === 0;
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};
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DoubleLinkList.prototype.size = function() {
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return this.length;
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};
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DoubleLinkList.prototype.getHead = function() {
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return this.head;
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};
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DoubleLinkList.prototype.getTail = function() {
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return this.tail;
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};
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const dll = new DoubleLinkList();
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console.log('Initialized an instance of DLL');
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dll.append(1).append(2).append(3).append(4);
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console.log(`Before insertAt : ${dll.toString()}`);
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dll.insertAt(23, 4);
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console.log(`After insertAt : ${dll.toString()}`);
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console.log('Removing element at index 3');
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dll.removeAt(3);
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console.log(`After removing element at index 3 : ${dll.toString()}`);
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dll.insertAt(45, 2);
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console.log(`After inserting 45 at index 2 : ${dll.toArray()}`);
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console.log(dll.toString());
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console.log(dll.delete(3));
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console.log(`After deleting element at index 3 : ${dll.toArray()}`);
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console.log(`Is DLL empty : ${dll.isEmpty()}`);
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console.log('Head of dll is : ');
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console.log(dll.getHead());
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console.log('Tail of dll is : ');
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console.log(dll.getTail());
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